Electric Charges, DC Circuits, Magnetism
1. Two point charges of charge +Q are placed as shown below. At what point will a
negative charge experience a force toward the bottom of the page?
a) A
b) B
c) C
d) D
e) E
2. Four point charges are placed in the corners of a square, as shown in the figure
below. If q
b
= 10
-9
C, q
c
= -10
-9
C and q
d
= 10
-9
C, and the magnitude of the electric
forces on q
c
is 0 N, which of the statements below is true?
a) q
c
> 10
-9
C
b) 0 < q
c
< 10
-9
C
c) q
c
= 0C
d) -10
-9
C < q
c
< 0C
e) q
c
< -10
-9
C
3. The magnitude of the electric field generated by a charge q at a distance d
1
from
the charge is E
1
. What is the magnitude of the electric field generated by the charge at
a distance d
2
from the charge?
a) E
1
b) E
1
·(d
2
2
/d
1
2
)
c) E
1
·(d
1
2
/d
2
2
)
d) E
1
·(d
1
/d
2
)
e) E
1
·(d
2
/d
1
)
4. What is the capacitance between the points A and B if C
1
= C
2
= C
3
= 10
-6
F?
a) 10
-6
F
b) 2·10
-6
F
c) .67·10
-6
F
d) .5·10
-6
F
e) 1.5·10
-6
F
5. A DC voltage source is connected to two resistors in series, as shown in the figure
below. What is the ratio between the power dissipation of resistor R
1
and the power
dissipation of resistor R
2
?
a) (R
1
/R
2
)
2
b) (R
2
/R
1
)
2
c) (1 - R
1
)/(1 - R
2
)
d) R
1
/R
2
e) R
2
/R
1
6. A copper wire of length l
1
= 6 m and cross-sectional area of A
1
= 4 mm
2
has the
same resistance as another copper wire of length l
2
= 18m. What is the ratio between
the masses of the two wires, m
2
/m
1
?
a) 9
b) 3
c) 1
d) 1/9
e) 1/3
7. A particle with a positive charge of q moves with a speed v and passes through a
magnetic field B parallel with the speed v. What is the magnitude of the magnetic
force on the particle?
a) F = qvB
b) F = -qvB
c) F = 0
d) F = qvB/2
e) F = -qvB/2
8. In the figure below, a magnetic field of .01 T is applied locally to a wire carrying a
current of intensity I = 10A. What is the magnitude of the magnetic force applied to
the wire?
a) F = .3N
b) F = .4N
c) F = .5N
d) F = 1N
e) F = 3N
9. Three parallel long straight wires carry currents as shown in the picture below. If
the currents in the wires #1 and #2 are I = 5A, and the magnetic force on wire #1 is
equal to 0A, what is the current in wire #3?
a) I
3
= 5A
b) I
3
= 10A
c) I
3
= 15A
d) I
3
= 20A
e) I
3
= 25A
10. Two metallic bars slide along metallic rails at speeds v
1
= .1m/s and v
2
= .2m/s as
shown below. The bar and the rails are situated in a magnetic field of 4T. What is the
induced voltage in the bar and rails?
a) 50mV
b) 60mV
c) 100mV
d) 120mV
e) 150mV
Solutions:
Question #1: b
Question #2: e
Question #3: c
Question #4: c
Question #5: d
Question #6: a
Question #7: c
Question #8: b
Question #9: d
Question #10: d
